Ask a Master Gardener: Digging into Soil Microbes

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Last week I had so much fun talking about dirt that I thought I’d dig a little deeper with some information on germs.

I used to get some respite from the cold, wintry weather when I thought it was killing the bugs that were killing my garden. But in recent years, I’ve learned from a few entomologists that insects may be doing better than me. Now I can only look out the window and hope for spring – that and start some plants indoors to give them a head start when it warms up.

Although bad bugs don’t die, neither do good ones. In fact, the incredible diversity of organisms that make up the soil food web slow down but continue to function throughout the winter. Their size varies from the smallest single-celled bacteria – algae, fungi and protozoa – to more complex nematodes and microarthropods, including earthworms, insects, small vertebrates and visible plants. As these organisms eat, grow, and move through the soil, they provide clean water, clean air, and healthy plants.

Here are some things you can do to help the microbes in the soil and give your garden a boost.

The first step is to control erosion and minimize soil disturbance. Every time you disturb the soil, whether with a shovel, tiller or plow, you expose it to the erosive forces of water and wind. Although some have discouraged soil disturbance since the days of the Dust Bowl, erosion remains a major problem today.

One of the best erosion control methods is to sow annual cover crops like oats and radishes immediately after harvest. They germinate and grow quickly, covering bare ground and stabilizing it against winter rains and high winds. There are many other benefits to using cover crops, from adding nitrogen to the soil to increasing organic matter, which brings us to the next step: maximizing organic matter.

Leaf litter, dying plants, decaying animals and the microbes themselves make up organic matter. Up to 50% of soil organic matter can come from microorganisms.

This is important because it is the interaction between dead plant matter, roots, minerals and microbes that creates stable, porous soil that can absorb water. And increasing organic matter is known to increase the number of good insects in the garden.

The next step is to increase the number and diversity of soil microbes. Increase microbial diversity by increasing plant diversity. Avoid planting the same plants in the same area year after year. Not only do you have to rotate your crops, but also try new ones regularly. And of course, if you use pesticides, do so sparingly and follow the directions on the container.

Our next course of action is to maximize water infiltration and retention. Again, plants are the answer, and the longer the root system the better. Deep-rooted native plants in particular will eventually loosen the soil, even stubborn clay, allowing for better infiltration and retention, so you may want to consider some native plants in your rotation schedule. Some municipalities specify native plants in their stormwater control projects to improve soil structure and its ability to absorb, hold, and slowly release water.

Cover crops are also ideal for this, although they will be plowed in the spring. The four-inch-tall annual ryegrass was found to have roots 21 inches deep.

Last but not least, we need to minimize soil compaction. Just like animals above ground, soil microbes need space and air in their environment to survive and thrive. Grinding their habitat with heavy equipment and continuous trampling (walking) compacts the soil and kills them. To keep your soil food web alive and healthy, minimize equipment in growing areas.

Late February is the time to start cabbage, broccoli, cauliflower, kale, etc. indoors to have beautiful seedlings ready for spring planting. Petunias and Coleus can also be declared now.

Happy gardening!

Peter Sutter is a lifelong gardening enthusiast and a participant in MU Extension’s Callaway County Master Gardener program. Gardening questions can be sent to [email protected]

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